1. Field of the Invention
The present invention relates to novel optically active isoxazole derivatives represented by general formula: ##STR3## which are useful as intermediates for synthesis of prostaglandin and a process for producing the same as well as intermediates for preparing the compounds [XI] described above and a process for preparation thereof. The optically active isoxazole derivatives [XI] in accordance with the present invention are then led to optically active 2-methylenecyclopentanone derivatives represented by general formula: ##STR4## which are important intermediates for synthesis of prostaglandins developed by G. Stork et al. (G. Stork, M. Isobe, J. Am. Chem. Soc., 97, 4745 (1975)). The 2-methylenecyclopentanone derivatives are further led to prostaglandin according to the method of Stork et al. described above.
In the formulae described above, R.sup.1 represents an alkyl group or a cycloalkyl group which may have an alkoxy group or a group shown by -Ra-A-B (wherein Ra is an alkyl group; A is a hetero atom or an single bond; and B is an aromatic or hetero ring which may have a substituent(s)); and R.sup.2 and R.sup.3, which may be the same or different, each represents an aralkyl group, a silyl group or an acyl group.
Prostaglandin (PGF and PGE) is a series of compounds having extremely potent physiological activities which is formed in vivo by chemical conversion of higher unsaturated fatty acids such as arachidonic acid, etc. by the action of enzyme for synthesis of prostaglandin and has the following chemical structures. ##STR5##
It is known that in natural prostaglandin, R' is n--C.sub.5 H.sub.11 -- and R is --(CH.sub.2).sub.6 COOH or --CH.sub.2 CH.dbd.CH(CH.sub.2).sub.3 COOH in the formulae above. It is also known that it is important for the group R' to be oleophilic in exhibiting its physiological activities. During the course of development and research on prostaglandin for its application to drugs, it has further been revealed that an alkyl group, a cycloalkyl group or an aralkyl group having 4 to 10 carbon atoms are effective as the group R'; an alkyl group such as pentyl, isopentyl, 2,2-dimethylpentyl, hexyl, 2-hexyl, heptyl, 2-ethoxy-1,1-dimethylethyl, 5-methoxy-1-methylpentyl, etc.; a cycloalkyl group such as cyclopentyl, 3-ethylcyclopentyl, 4-propylcyclohexyl, etc.; and groups such as phenyloxymethyl, 3-trifluoromethylphenyloxymethyl, 2-chlorothiophen-5-yloxymethyl, furan-2-yl-2-ethyl, etc. exert on potent physiological activities. The compounds of the present invention are useful as starting materials which can introduce substituents including these organic groups into the desired compounds.
2. Description of the Prior Art
As routes for preparing optically active prostaglandin, a process starting from Corey lactone and a process starting from 4-hydroxycyclopentenone are hitherto known. However, according to the former process, many steps should be required and as a matter of course, yield of the final product decreases. In the latter process, a problem that it is relatively difficult to set reaction conditions for preventing side reactions but predominating the main reaction over the side ones remains unsolved. The aforesaid process developed by G. Stork et al., namely, the process which comprises preparing 2-methylenecyclopentanone derivatives [XIII] as intermediates and leading the intermediates to prostaglandin is useful in that stable compounds [XIII] are used as intermediates; however, the intermediates [XIII] obtained by this process take a racemic form but no optically active compounds are obtained.
As a result of extensive investigations to solve the problems described above, the present inventors have found a process for preparing optically active 2-methylenecyclopentanone derivatives [XIII] in a simple manner and high yield which are key intermediates for production of prostaglandin. The present invention thus provides novel intermediates obtained during the course of preparing the compounds [XIII] and a process for preparation thereof.